Vesicular stomatitis virus (VSV) is a negative stranded RNA virus which infects most mammalian cells and expresses viral proteins up to 60% of total proteins in infected cells [Kim, G. N., and C. Y. Kang. Virology 357:41, 2007]. In nature VSV infects pigs, cattle, and horses, and causes vesicular disease around the mouth and foot. Although human infection by VSV has been reported, VSV does not cause any serious symptoms in humans [Fields, B. N., and K. Hawkins. N Engl J Med 277:989, 1967; Johnson, K. M. et al. Am J Trop Med Hyg 15:244, 1966].
VSV encodes five proteins, nucleocapsid protein (N), phosphoprotein (P), matrix protein (M), surface glycoprotein (G), and RNA dependent RNA polymerase (L). The N, P, and L proteins of VSV are required for synthesis of positive sense and negative sense genomic RNAs and mRNA, which are necessary for the synthesis of VSV proteins.
Blocking the host cellular protein synthesis by VSV matrix (M) protein induces cell death. Changing a methionine residue at position 51 of the M protein to arginine (M51R) in the vesicular stomatitis virus Indiana serotype (VSVInd), and changing methionines at position 48 (Met48) and 51 (Met51) to Arg in the vesicular stomatitis virus New Jersey serotype (VSVNJ) M gene could negate this function of VSV M protein (Kim, G. and Kang, C., Virology, 357:41-53, 2007). While the VSVs with these Met to Arg mutations in the M protein have significantly reduced cytopathic effects, they still replicate and produce progeny viruses in the cell and in the infected animal. One of the temperature sensitive (ts) M gene mutants of VSVInd Orsay strain, tsO23 has shown limited replication in a mouse glial cell line at 37° C. and 39° C. (Rabinowitz, S. et al. Infection and Immunity 33:120-125, 1981). It has been demonstrated that the temperature sensitivity of tsO23 was the result of the improper or lack of the initiation of the viral assembly with the characteristic bullet shaped structure at 39° C. (Flood, E. et al. Virology 278:520-533, 2000; Lyles, D. et al. Virology, 217:76-87, 1996). In addition, the tsO23 lost its neurovirulence in mice even after direct inoculation into the brain (Rabinowitz, S. et al. Infection and Immunity, 33:120-125, 1981).
There are three amino acid differences between wild type M of VSV Orsay strain and M of tsO23, which are glycin (G) to glutamic acid (E) at 21st amino acid (G21E), leucine (L) to phenylalanine (F) at 111th amino acid (L111F), and histidine (H) to tyrosine (Y) at 227th amino acids (H227Y) (Morita, K. et al. J. Virol. 61:256-263, 1987). The single amino acid reversion at F111 to L in revertants implicated that the F111 appears to play a major role in the temperature sensitivity of the tsO23. However, the other two mutations may also have some role because the single reversion from the F to L at 111th position did not recover the virus completely to its wild type phenotype (Morita, K. et al. J. Virol. 61:256-263, 1987; Li, Y. et al. J. Virol. 62:3729-3737, 1988).
Currently, research groups have developed replication competent, assembly defective VSV having a G glycoprotein (G) gene deleted (AG) or both G and M genes deleted (AMG) as safer vaccine vectors (Kahn, J. et al. J. Virol. 75:11079-11087, 2001; Schwartz, J. et al., Virology 366:166-73, 2007). However, having the G gene deleted or M and G gene deleted, the VSV vector requires the supply of G or both M and G proteins in trans for the production of the assembly-defective VSV. In order to reduce the cost of producing vaccines, it is necessary to generate a system, which can produce the viral vaccine vectors that can replicate in high titre. Therefore, what is needed is a full-length VSV vector system, which has lost its virulence (avirulent) and still can replicate to a high titer in vitro at 31° C. cannot assemble properly at non-permissible temperatures, and induce good immune responses against the gene of interest that it expresses.
Further and other objects of the invention will be realized from the following Summary of the Invention, the Discussion of the Invention and the embodiments and Examples thereof.